Propionate transport in rat liver cells

Area of Science:

• Biochemistry
• Cell Biology
• Hepatology

Background:

• Hepatic extraction of propionate is highly efficient, suggesting a specific transport mechanism across the hepatocyte membrane.
• Understanding propionate uptake is key to comprehending its role in hepatic metabolism and gluconeogenesis.

Purpose of the Study:

• To characterize the kinetic and regulatory properties of propionate transport in isolated hepatocytes.
• To investigate the physiological relevance of identified transport components in vivo.

Main Methods:

• Utilized [14C]propionate to measure uptake in isolated rat hepatocytes under controlled metabolic conditions.
• Assessed the effects of varying substrate concentrations, pH, and inhibitors on propionate transport kinetics.
• Correlated in vitro findings with in vivo hepatic propionate uptake data.

Main Results:

• Identified a high-affinity (Km ≈ 0.15 mM) carrier-mediated propionate transport system in hepatocytes.
• This system is not Na+-dependent, not concentrative, and unaffected by acetate or butyrate.
• Uptake is inhibited by halogenated monocarboxylates and sensitive to extracellular pH, being stimulated by acidic conditions.
• In vivo hepatic uptake is nearly quantitative at physiological plasma concentrations, consistent with the high-affinity component's capacity.

Conclusions:

• Hepatic propionate uptake is primarily mediated by a specific, high-capacity carrier system.
• This carrier-mediated transport is unlikely to be the rate-limiting step for hepatic propionate utilization under physiological conditions.